An insertion instrument (10) is provided including a tube (12) having a proximal end (14) adapted to be gripped by a user and a distal end (16) adapted for insertion. A tip control actuator (20) is located at the proximal end (14), and the distal end (16) of the tube (12) includes a flexible portion (30). This flexible portion (30) includes a spine (32) and a plurality of circumferentially extending ribs (34) extending from the spine (32). The ribs (34) are axially spaced apart from a distal tip (38) toward the proximal end (14), with the ribs (34) being spaced apart by wedge shaped partial circumferential openings (40). The ribs (34) have first (35) and second (36) axial sides defined by the wedge-shaped openings (40), with the first axial side (35) of one of the ribs (34) facing the second axial side (36) of an adjacent one of the ribs (34). For each of the ribs (34), at least one of the first (35) or second (36) axial sides includes at least one of an axially extending projection (50) or a recess (52) and a facing one of the at least one of the first (35) or second (36) axial sides of an adjacent one of the ribs (34) includes at least one of a complementary mating recess (51) or a corresponding axial projection (53). At least one tension wire (60) extends from the tip control actuator (20) to the distal tip (38).
